1. Technical Field
The present disclosure relates to an electrostatic chuck and a substrate temperature control fixing apparatus including the electrostatic chuck. More particularly, the present disclosure relates to an electrostatic chuck for holding an object mounted on a base and a substrate temperature control fixing apparatus including the electrostatic chuck.
2. Related Art
The film forming apparatus (e.g., the CVD apparatus, the PVD apparatus) and the plasma etching machine used in manufacturing a semiconductor device such as IC or LSI is equipped with a stage to hold a substrate (e.g., silicon wafer) in a vacuum processing chamber with good precision. As such stage, a substrate temperature control fixing apparatus equipped with an electrostatic chuck, for example, has been proposed. The substrate temperature control fixing apparatus attracts and holds the substrate with the electrostatic chuck, and performs a temperature control such that the substrate is maintained at a predetermined temperature.
FIG. 1 is a schematic plan view showing a substrate temperature control fixing apparatus in the related art. FIG. 2 is a schematic sectional view showing the substrate temperature control fixing apparatus in the related art, and taken along a II-II line in FIG. 1. By reference to FIG. 1 and FIG. 2, a substrate temperature control fixing apparatus 100 has an electrostatic chuck 101, an adhesive layer 105, and a base plate 106.
The electrostatic chuck 101 is the Coulomb force type electrostatic chuck or the Johnson-Rahbek type electrostatic chuck having a base 102 and electrostatic electrodes 103. The base 102 is fixed on the base plate 106 via the adhesive layer 105. The base 102 is formed of ceramic. The base plate 106 is formed of Al. The adhesive layer 105 secures the base 102 and the base plate 106. As the adhesive layer 105, the silicon adhesive is used.
An outer peripheral sealing ring 102b as an annular projection portion, when viewed from the top, is provided on an outer edge portion of an upper surface 102a of the base 102. A large number of projection portions 102c shaped into a cylindrical column respectively are provided on the inner side of the outer peripheral sealing ring 102b such that they are dotted like a polka dots pattern, when viewed from the top.
The electrostatic electrodes 103 are formed of a thin film electrostatic electrode respectively, and are built in the base 102. The electrostatic electrodes 103 are connected to a DC power supply (not shown) provided outside of the substrate temperature control fixing apparatus 100. When a predetermined voltage is applied, the electrostatic electrodes 103 attracts and holds an object (not shown) such as a substrate on upper surfaces of the outer peripheral sealing ring 102b and the large number of projection portions 102c. A chucking force becomes stronger as the voltage applied to the electrostatic electrodes 103 is increased higher.
The base plate 106 is provided to support the electrostatic chuck 101. A heating element (not shown) and a water channel 104 are provided to the base plate 106 to perform the temperature control of the base 102. The heating elements (not shown) generate a heat when the voltage is applied thereto, and heats the base 102 via the adhesive layer 105.
The water channel 104 has a cooling water inlet 104a and a cooling water outlet 104b, each of which is formed in a lower surface 106b of the base plate 106. The cooling water inlet 104a and the cooling water outlet 104b are connected to a cooling water controlling unit (not shown) provided on the outside of the substrate temperature control fixing apparatus 100. The cooling water controlling unit (not shown) introduces the cooling water into the water channel 104 via the cooling water inlet 104a, and exhausts the cooling water from the cooling water outlet 104b. The cooling water is circulated to cool the base plate 106 and thus cool the base 102 via the adhesive layer 105.
A gas channel 108 is formed in the base 102, the adhesive layer 105, and the base plate 106 to pass therethrough. The gas channel 108 has a plurality of gas inlets 108a formed in the lower surface 106b of the base plate 106, and a plurality of gas outlets 108b formed in the upper surface 102a of the base 102. A plurality of gas inlets 108a are connected to a gas pressure controlling unit (not shown) provided out of the substrate temperature control fixing apparatus 100. The gas pressure controlling unit (not shown) can vary a pressure of an inert gas in a range of 0 to 50 Torr, for example, and can introduce an inert gas into the gas channel 108 from the gas inlets 108a. 
FIG. 3 is a schematic plan view showing a state that the related-art substrate temperature control fixing apparatus attracts and holds the substrate. In FIG. 3, the same reference symbols are affixed to the same components as those in FIG. 1 and FIG. 2, and their explanation will be omitted in some cases. In FIG. 3, 107 denotes a substrate, and 109 denotes a gas filling portion in which an inert gas is filled. By reference to FIG. 3, the substrate 107 is attracted and held on the upper surfaces of the outer peripheral sealing ring 102b and a large number of projection portions 102c of the base 102. A temperature of the substrate 107 is controlled by the heating element (not shown) and the water channel 104, which are built in the base plate 106.
The gas pressure controlling unit (not shown) introduces an inert gas into the gas channel 108 through a plurality of gas inlets 108a. The introduced inert gas is exhausted from the gas outlets 108b. When the inert gas is filled in the gas filling portions 109 formed between the substrate 107 and the upper surface 102a of the base 102, a thermal conductivity between the base 102 and the substrate 107 is improved. The outer peripheral sealing ring 102b is provided to prevent such an event that the inert gas filled in the gas filling portions 109 leaks to the outside of the gas filling portions 109.
As described above, the related-art substrate temperature control fixing apparatus 100 attracts and holds the substrate 107 on the upper surfaces of the outer peripheral sealing ring 102b and the large number of projection portions 102c of the base 102 of the electrostatic chuck 101. Also, the outer peripheral sealing ring 102b, which is formed as the annular projection portion, when viewed from the top, is provided on the outer edge portion of the upper surface 102a of the base 102 in the related-art substrate temperature control fixing apparatus 100. Thus, the outer peripheral sealing ring 102b prevents such an event that the inert gas, which is filled in the gas filling portions 109 to improve a thermal conductivity between the base 102 and the substrate 107, leaks to the outside of the gas filling portions 109. Also, the heating element (not shown) and the water channel 104, which are built in the base plate 106 in the related-art substrate temperature control fixing apparatus 100, control a temperature of the base plate 107 (see JP-A-2000-317761 and JP-A-2000-332091, for example).
However, the silicon adhesive constituting the adhesive layer 105 has a low plasma resistance. Therefore, when the related-art substrate temperature control fixing apparatus 100 is used in the plasma, the adhesive layer is exposed into the plasma and is corroded. When the adhesive layer 105 is eroded, the inert gas leaks through the eroded portion, and thus a thermal conductivity between the base 102 and the substrate 107 is degraded. Also, the plasma cleaning is applied to remove attached substances deposited on the upper surface 102a of the base 102. In this case, the plasma used in the cleaning not only removes the attached substances but also corrodes the upper surface 102a of the base 102.
When the adhesive layer 105 and the upper surface 102a of the base 102 are eroded by the plasma, degradation of the substrate temperature control fixing apparatus 100 is caused. At that time, the maintenance should be done by applying a renewal polishing or a cleaning using chemicals, or the like to the upper surface 102a of the base 102 or by replacing the over-all substrate temperature control fixing apparatus 100 with the new one. In this case, such a problem existed that a predetermined cost is needed in doing the maintenance and also an availability factor of the apparatus is lowered.